Means for controlling the draft in furnace flues



V N 9 w. a. TRETHEWEY 05 MEANS FOR CONTROLLING THE DRAFT m FURNACE FLUES7 Filed July 19, 1938 3 Sheets-Sheet 1 J, S t H h H 4 a .1 m A. v B M 11 1 mm s, 194

w. B. TRETHEWEY MEANS FOR CONTROLLING THE DRAFT IN FURNACE FLUES FiledJuly 19, 1938 3 Sheets-Sheet 2 a TREZTHEWEY Z2Z10,63 mums FOR qou-x koL-Ike THE mum m FURNACE mugs Nov. 5, 1940 a sheets-shat a Filed July 19,1938' Patented Nov. 5, 1940 UNITED STATES.

DIEAN S FOR WNTROILING THE DRAFT IN FURNACE FLUES William BertramTrethewcy, Haywards Heath, England, assignor to Furnace ControlsLimited,

London, England Application July 19, 1938, Serial No. 220,6 In GreatBritain July 20, 1937 4 Claims.

This invention relates to automatic regulators, for controlling thedraft in a flue, oi the type comprising a thermostat positioned in theflue, a damper system, which is operable to control the draft in theflue, by checking the flow oi hot gases through the flue andsimultaneously admitting atmospheric air to the flue through an inlet inthe side wall thereof, and an operative connection between thethermostat and the damper system arranged to'position the latter so asto maintain a substantially constant temperature in the flue. With sucha regulator, if the temperature of the flue gases should rise, thethermostat will move the damper system towards the minimum position,thereby admiting more air to the flue and reducing the draft through theflue. and ii the temperature of the flue gases should fall, thethermostat will move the damper system towards the maximum position,thereby reducing the air U supply and increasing the draft through theflue. A single damper may be employed to control both the air flow andthe flow of hot gases'through the flue, but it is equally possible to dothis by means of a pair oi interlinked dampers, one controlling the airinlet and the other the flow of hot gases through the flue.

When such a regulator is in use, it is sometimes diflicult to eii'ectrapid heating up or a furnace associated with the fire. owing to the atendency of the device to maintain in the flue a constant temperaturelower than that required for rapid heating. 1

The object of this invention is to overcome this difliculty and toprovide means whereby the fur- I5 nace may be rapidly heated up whenrequired.

The present invention provides an automatic regulator of the typedescribed above, which includes means operable at will to reduceartificially the working temperature of the thermostat below 40 itsnormal working temperature.

, Thus the apparatus may includemeans operable to admit to thethermostat a secondary supply of air through a port in the wall of theflue, which secondary supply of air will reduce the 45 workingtemperature of the thermostat and so cause it to move the damper systemtowards the maximum position and draw the fire up.

In one form of automatic regulator according to the invention, theregulator is provided with a 50 shield, which is normally inoperative,but is movable at will into position to shield the thermostat from theflue gases approaching from the furnace, and which, when moved into itsoperative position. opens a port in the flue through which .56 coolingair may pass to the thermostat.

By moving the shield into its operative position the thermostat will beprotected from the hot gases coming from the furnace'with the resultthat the thermostat will be kept cool and hold the damper system in themaximum position. Gone 5 sequently, the iurnace can be rapidly heated upand this is of particular advantage where the automatic regulator isused in conjunction with a furnace for heating a domestic hot watersystem, or for lighting the fire of any heater. Once it) the fire isproperly alight it is oi course desirable that the automatic regulatorshould once more take control and to this end the shield should bereturned to its normal imperative position. This may be done by hand,but if desired may be el'- 5 fected automatically by means 01 athermostat responsive to the temperature oi the water in the hot watersystem, so that once the water has reached a predetermined temperaturethe shield will be withdrawn and enable the thermostat and the automaticregulator to take over the control of the gases in the flue.

The water temperature can, therefore, be used to control the temperatureof the flre. When the water is cold and rapid heating is required, theshield is automatically placed in operative position, with the resultthat a high furnace temperature will prevail. When the water, however,is sufliclently heated, the shield is withdrawn, allowing the thermostatto resume control and reduce the i'umace temperature to normal again. Inthe preferred form oi the invention, the thermostat is mounted so as tobe movable relatively to the flue into a position in which it is notexposed to the direct action of the flue gases. 86 Thus it may becarried on a pivoted arm which can be moved, by a control outside theflue, so as to swing the thermostat from its normal position to aposition in which it is located in a recess to the side of the flue.With the thermostat in its nor- 0 mal position it is fully exposed tothe hot gases and will position the damper system to give a minimum fluetemperature. In the latter position the thermostat will be shielded fromthe direct influence oi the gases,'. and will therefore adjust thedamper system to give a maximum flue temperature. Obviously intermediatetemperatures may be obtained by setting the thermostat arm to positionsbetween these two extremes.

It is preferred to provide in the wall or the recess a supplementary airinlet for the purpose or cooling the thermostat when the latter is movedinto the recess.

In known thermostat controls for flues, the

thermostat is generally placed under an initial 56 tension so as toprevent it from actuating the damper system until the flue gases havereached a given temperature. By adopting this invention, the use of suchinitial tension is no longer essential, as the temperature of thethermostat can be artificially reduced while the flue is heating up, andthe means for eflecting such artificial reduction of the thermostattemperature can be rendered inoperative'when it is required that thethermostat should assume control.

Some constructions of automatic regulator according to the inventionwill now be described in further detail, by way of example, withreference to the accompanying drawings, in which:

Figure 1 is a vertical section through the first construction ofregulator showing the parts in the position they occupy when thethermostat is in control;

Figure 2 is a similar view but showing the parts in the position theyoccupy when the temperature of the thermostat is artificially reduced;

Figure 3 is aside elevation of the second construction;

Figure 4 is the corresponding plan view;

Figure 5 is a section along the line V-V in Figure 4, and

Figure 6 is a detail view, similar to Figure 5, of a modifiedarrangement.

Like references indicate like parts throughout the drawings.

In the construction shown in Figures 1 and 2, iii represents the fiue inwhich is positioned a thermostat H, constituted by a bimetallic stripcoiled in the form of a spiral with its one end attached to a spindle l2and its other end attached to an anchor member I3, within which thespindle is rotatably mounted. In the wall of the flue is provided aninlet ll for atmospheric air, this inlet being controlled by a damper I!which also serves to control the flow of hot gases through the flue. Onthe end of the spindle 12 a crank it is formed which is connected by alink I1 to a crank arm l8 formed on one end of the hinge pin to whichthe damper I5 is secured. Rotation of the spindle i2, caused by theexpansion or construction of the bimetallic strip, will therefore effectrotation of the damper i5 about the axis of the hinge in the directionrequired to maintain a constant temperature in the flue. The anchormember i3 is provided with a spring pressed pin [9 held in contact withthe member I3 and forming a friction brake which normally holds theanchor member against movement relatively to the flue but is arranged toyield and permit the anchor member to turn to avoid straining of thethermostat in case the latter should be overheated.

To an aperture in the flue opposite the end of the thermostat, is fitteda side tube provided with ports 2| for admitting a secondary supply ofair to the thermostat. These ports are normally closed by a shield 22which is slidable within the side tube 20. When the thermostat is toassume control of the temperature in the flue, the shield 22 occupiesthe inoperative position shown in Figure 1 in which the thermostat isfully exposed to the action of the flue gases and in which the ports 2|are closed. When, however, it is desired artificially to reduce theworking temperature of the thermostat, for example in order tofacilitate rapid heating up of the furnace, the shield 22, forming ascreening element, can be moved into the position shown in Figure 2 inwhich it protects the thermostat from the action of the line gases andin which the ports 2| are opened to deliver a secondary supply of air tocool the thermostat. As will be seen, the effect of this artificialcooling of the thermostat is to move the damper i5 into the closedposition shown in Figure 2, in which it no longer checks the DB5- sagefor the flue gases and in which it permits only a very limited supply orair to enter the inlet M.

In the second construction shown in Figure 3-8, the thermostat II islikewise of spiral form but is arranged to actuate two'dampers I5, 25,the damper l5 controlling the air inlet H and the damper controlling thepassage for the flue gases.

The thermostat l I is constituted by a spiral bimetallic strip attachedat one end to a block fixed to the thermostat spindle 12 by an adjustingscrew 4!. The other end of the strip is attached to a crank arm 42carrying an extension 23 connected by a link 24 to the damper 25. By

slackening the screw 4! and adjusting the block 40 relatively to thespindle l2, the tension of the thermostat can be varied.

The damper 25 is connected by a link 26 to the damper l5. Rotation ofthe crank arm 42 by the thermostat II will, therefore, eii'ectsimultaneous actuation of the two dampers i5, 25. The entire system ofdampers, thermostat and actuating linkages is carried on a casting 21fixed over a cutaway portion of the flue Iii-by wing nuts 50.

To a cranked extension 20 of the spindle I2 is fixed an arm 29 which islocated outside the wall of the fiue and which is movable to vary theposition of the damper relatively to the flue gases. In the position ofthe arm designated as "0001 in the scale shown in Figure 3, thethermos'tat will occupy the position shown in'chaindotted lines inFigure 5. Here, the thermostat being fully exposed to the flue gases, itwill operate to maintain a cool temperature in the flue. On movement ofthe arm through the "medium" into the "hot position, the thermostat isbrought into the full line position in Figure 5. Here it is lessexposedto the hot gases and more to the air entering through the inlet I4, andso will act to maintain a higher temperature in the fiue. Owing to thefact that the cranked extension 28 is larger than the link 22, theeffect of moving the thermostat towards the hot position is to impose anincreased tension on it, thus giving it a further tendency to maintain ahot fire and a wider range of temperatures through which it willoperate.

At the side of the casting 21 a shield 3|, forming a screening element,is provided. This shield forms a recess 32 in the side wall 3. When thearm 29 is moved to the light non-auto" position, the thermostat isbrought into this recess, as shown by dotted lines in Figure 5. This isthe position to which the thermostat is moved when it is desired to heatthe flue rapidly, as when lighting the fire, and here the thermostat isnot exposed to the flue gases at all. In order to assist in cooling thethermostat when in this position, a supplementary air inlet 35 isprovided, through which air will enter the recess 22 when the damper I5is open.

In the modified arrangement shown in Figure 6, a shutter 33 normallycloses the recess 32, but when the thermostat is moved into the recessit strikes against and displaces a pin 34 secured to the shutter andtherefore opens the shutter to admit secondary air into the recess tocool the thermostat, as indicated by the dotted lines.

It will be appreciated that, if desired, the arm 28 could be arranged tobe operated by a further master thermostat responsive to thewater-temperature in a hot water system associated with the furnace towhich the regulator is fitted. In this way the arm 29 wouldautomatically take up the position required to correct a fall in thewater temperature due to the withdrawal of hot water from the system.

What I claim as my invention and desire to secure by Letters Patent is:

1. An automatic regulator for controlling the draft in a flue,comprising a thermostat positioned in the flue, a damper system in theflue for controlling the draft, an operative connection between thethermostat andpthe damper system. a screening element for saidthermostat, a pivoted arm carrying said thermostat, and a control forsaid pivoted arm arranged outside the flue,

the thermostat element, and a mounting for said thermostat which isoperable fromthe exterior of the flue to move the thermostat bodilyacross the flue and in a. direction transverse to the lengthof thethermostat from a position which it is clear of said recess into apofltionjiiiu which it lies in said recess. ;1

3. An automatic regulator for controlling. the draft in a flue,comprising a thermostat positioned in the flue, a damper system in theflue for controlling the draft in the flue and the admissionof asupplementary supply of air thereto, an operative connection between thethermostat and the damper system and a mounting for said thermostatwhich is operable from the exterior of the flue to move the thermostatbodily across the flue in a direction transverse to the length of thethermostat from a position in which it is exposed to the direct actionof the flue gases into a series of positions in which it is increasinglyexposed to the action of the supplementary air.

4. A device for controlling the draft in a flue having an inlet foratmospheric 'air. comprising a casing adapted to fit over said inlet andshaped to form a recess to the side of the flue when fitted thereto, anarm pivoted to said casing and pro- Jecting from the inner face thereof,a thermostat carried on said arm, a damper system mounted on the casingand serving to control the flow of gases in the flue and the passage ofair through said inlet, an operative connection between the thermostat ad the damper system arranged to position the atter so as to maintain aconstant flue temperature determined by the position of the thermostatrelatively to the flue, and an ac tuating member external to the casingfor rotating the arm about its pivot and thereby moving the thermostatbodily in relation to the casing in a direction transverse to thelength'of the thermostat for the purpose of varying the temperaturemaintained by the thermostat in the flue.

WILLIAM BERTRAM 'IRETHEWEY.

